An echo IC currently used in karaoke related products uses an SRAM to store audio information for the delay effect. However, each cell of the echo IC needs 6 transistors, as shown in FIG. 1, including 2 PMOS transistors and 4 NMOS transistors. An echo IC can not be miniaturized with so many transistors. Also because of different structures between PMOS and NMOS, the manufacturing process is complicated, and the cost cannot be reduced.